The major task of our investigation is to study electron aspects of interaction of antitumor compounds with the cell components. At present, some nitrosourea derivatives are of significant interest. Methylnitrosourea (MNU) is the most effective antitumor compound used in therapy [ 1-31. This paper gives the results of investigation of MNU electron structure observed by ESR and quantum-chemical methods. To elucidate the nature of MNU chemical activity the nitrosourea derivatives, which are not effective inhibitors of tumor growth, were also studied. The MNU electron structure data proved to be useful in clearing up the mechanism of interaction between MNU and DNA bases. The electron structure of MNU molecule and its ion radicals were calculated by INDO means. In this program the spatial coordinates of all atoms were calculated by ECM from the predetermined values of valency links, valency angles, and dihedral angles. Geometrical parameters of molecules were chosen from the table of standard geometrical parameters [4]. The angles between valency links are: for trihedral hybridization-120", for the tetrahedral one-109.5". All structures are planar with the exception of the following: (i) in molecule I the bond C7-H8 is perpendicular to the molecule plane; the C7-HI0 and C7-H9 bonds make the angle of 30" toward the molecular plane; (ii) in molecule I1 the angle N1C203 is 135"; (iii) in molecule I11 the bond C7-Cio is perpendicular to the molecular plane and the C7-Hs bonds make the angle of 30" toward the molecular plane. The comparison of differences in electron structure of MNU and ,its derivatives should be valid since the geometry of these molecules was chosen on the basis of equal assumptions.I. Methylnitrosourea 11. Nitrosourea (NU)

The problem of the sS content in the nucleon is discussed. In the framework of the generalized NambuJona-Lasinio model we estimate the parameter p of the Zweig rule violation and the critical temperature T, of the chiral-symmetry restoration.

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